使用multiprocessing解决PyMuPDF不支持多线程加载导致的界面卡死无响应问题，及一个PyQt5实现的简易PDF阅读器例子

最近在用PyMuPDF实现一个PDF阅读器，发现PyMuPDF在加载某些epub时耗时非常长，有的长达10几秒，会导致界面卡死无响应。

尝试用多线程后台加载，发现还是不能解决问题，和作者交流（issue链接 fitz.open blocks main thread even though I use it in a thread）后，作者说该库不支持真正的多线程，在多线程模式下也会阻塞主线程。

最后用multiprocessing解决该问题，我另外写了一个简单的PyQt5实现的PDF阅读器来说明如何解决该问题，效果图及代码如下。

#!python3
# -*- coding: utf-8 -*-
# this script demostrates how to use PyMuPDF in multiprocessing to avoid unresponsive GUI when fitz.open costs a long time
# author: yinkaisheng@live.com
import os
import sys
import time
import multiprocessing as mp
import queue
import fitz
from PyQt5 import QtCore, QtGui, QtWidgets

class DocForm(QtWidgets.QWidget):
    def __init__(self):
        super().__init__()
        self.process = None
        self.queNum = mp.Queue()
        self.queDoc = mp.Queue()
        self.pageCount = 0
        self.curPageNum = 0
        self.lastDir = ''
        self.timerSend = QtCore.QTimer(self)
        self.timerSend.timeout.connect(self.onTimerSendPageNum)
        self.timerGet = QtCore.QTimer(self)
        self.timerGet.timeout.connect(self.onTimerGetPage)
        self.timerWaiting = QtCore.QTimer(self)
        self.timerWaiting.timeout.connect(self.onTimerWaiting)
        self.initUI()

    def initUI(self):
        vbox = QtWidgets.QVBoxLayout()
        self.setLayout(vbox)

        hbox = QtWidgets.QHBoxLayout()
        self.btnOpen = QtWidgets.QPushButton('OpenDocument', self)
        self.btnOpen.clicked.connect(self.openDoc)
        hbox.addWidget(self.btnOpen)

        self.btnPlay = QtWidgets.QPushButton('PlayDocument', self)
        self.btnPlay.clicked.connect(self.playDoc)
        hbox.addWidget(self.btnPlay)

        self.btnStop = QtWidgets.QPushButton('Stop', self)
        self.btnStop.clicked.connect(self.stopPlay)
        hbox.addWidget(self.btnStop)

        self.label = QtWidgets.QLabel('0/0', self)
        self.label.setFont(QtGui.QFont('Verdana', 20))
        hbox.addWidget(self.label)

        vbox.addLayout(hbox)

        self.labelImg = QtWidgets.QLabel('Document', self)
        sizePolicy = QtWidgets.QSizePolicy(QtWidgets.QSizePolicy.Preferred, QtWidgets.QSizePolicy.Expanding)
        self.labelImg.setSizePolicy(sizePolicy)
        vbox.addWidget(self.labelImg)

        self.setGeometry(100, 100, 500, 600)
        self.setWindowTitle('PyMuPDF Document Player')
        self.show()

    def openDoc(self):
        path, _ = QtWidgets.QFileDialog.getOpenFileName(self, "Open Document", self.lastDir,
                    "All Supported Files (*.pdf;*.epub;*.xps;*.oxps;*.cbz;*.fb2);;PDF Files (*.pdf);;EPUB Files (*.epub);;XPS Files (*.xps);;OpenXPS Files (*.oxps);;CBZ Files (*.cbz);;FB2 Files (*.fb2)", options=QtWidgets.QFileDialog.Options())
        if path:
            self.lastDir, self.file = os.path.split(path)
            if self.process:
                self.queNum.put(-1) # use -1 to notify the process to exit
            self.timerSend.stop()
            self.curPageNum = 0
            self.pageCount = 0
            self.process = mp.Process(target=openDocInProcess, args=(path, self.queNum, self.queDoc))
            self.process.start()
            self.timerGet.start(40)
            self.label.setText('0/0')
            self.queNum.put(0)
            self.startTime = time.perf_counter()
            self.timerWaiting.start(40)

    def playDoc(self):
        self.timerSend.start(500)

    def stopPlay(self):
        self.timerSend.stop()

    def onTimerSendPageNum(self):
        if self.curPageNum < self.pageCount - 1:
            self.queNum.put(self.curPageNum + 1)
        else:
            self.timerSend.stop()

    def onTimerGetPage(self):
        try:
            ret = self.queDoc.get(False)
            if isinstance(ret, int):
                self.timerWaiting.stop()
                self.pageCount = ret
                self.label.setText('{}/{}'.format(self.curPageNum + 1, self.pageCount))
            else:#tuple, pixmap info
                num, samples, width, height, stride, alpha = ret
                self.curPageNum = num
                self.label.setText('{}/{}'.format(self.curPageNum + 1, self.pageCount))
                fmt = QtGui.QImage.Format_RGBA8888 if alpha else QtGui.QImage.Format_RGB888
                qimg = QtGui.QImage(samples, width, height, stride, fmt)
                self.labelImg.setPixmap(QtGui.QPixmap.fromImage(qimg))
        except queue.Empty as ex:
            pass

    def onTimerWaiting(self):
        self.labelImg.setText('Loading "{}", {:.2f}s'.format(self.file, time.perf_counter() - self.startTime))

    def closeEvent(self, event):
        self.queNum.put(-1)
        event.accept()

def openDocInProcess(path, queNum, quePageInfo):
    doc = fitz.open(path)
    quePageInfo.put(doc.pageCount)
    while True:
        num = queNum.get()
        if num < 0:
            break
        page = doc.loadPage(num)
        pix = page.getPixmap()
        quePageInfo.put((num, pix.samples, pix.width, pix.height, pix.stride, pix.alpha))
    doc.close()
    print('process exit')

if __name__ == '__main__':
    app = QtWidgets.QApplication(sys.argv)
    form = DocForm()
    sys.exit(app.exec_())